American Journal of Electromagnetics and Applications 2015; 3(6): 38-42
Published online October 14, 2015 (http://www.sciencepublishinggroup.com/j/ajea)
doi: 10.11648/j.ajea.20150306.11
ISSN: 2376-5968 (Print); ISSN: 2376-5984 (Online)
Miniaturized Ultra Wideband Microstrip Antenna Based on a Modified Koch Snowflake Geometry for Wireless Applications
Hafid Tizyi1, Abdellah Najid
1, Fatima Riouch
1, Abdelwahed Tribak
1, Angel Mediavilla
2
1STRS Lab., National Institute of Posts and Telecommunications–NIPT, Rabat, Morocco 2DICOM, University of Cantabria, Santander, Spain
Email address: [email protected] (H. Tizyi)
To cite this article: Hafid Tizyi, Abdellah Najid, Fatima Riouch, Abdelwahed Tribak, Angel Mediavilla. Miniaturized Ultra Wideband Microstrip Antenna Based
on a Modified Koch Snowflake Geometry for Wireless Applications. American Journal of Electromagnetics and Applications.
Vol. 3, No. 6, 2015, pp. 38-42. doi: 10.11648/j.ajea.20150306.11
Abstract: This paper presents a compact micro-strip patch antenna for ultra wideband (UWB) applications using a Koch
Snowflake fractal radiating antenna. The antenna supports two ultra widebands. For the lower band, a good impedance
bandwidth of 6.55GHz has been achieved from 3.4892GHz to 10.0392GHz. While the upper band covers 5.4976GHz (from
10.9013GHz to 16.3989GHz). It is fed by a 50Ω micro-strip transmission line with an overall size of 30x27 mm. The
simulation was performed by Computer Simulation Technology (CST) MICROWAVE STUDIO software, and compared with
High Frequency Structural Simulator (HFSS) software. The results show that the proposed antenna has interesting
characteristics for UWB applications.
Keywords: Ultra Wideband Antenna, Fractal Antenna, Koch Snowflake
1. Introduction
Antenna became a part of electrical devices in wireless
communication systems since 1888. The Ultra Wide Band
(UWB) technology opens new doors for wireless
communication systems. It plays a dominant role in
communication systems since the antenna is a key
component for wireless communication systems.
Since the Federal Communications Commission (FCC)
allowed [3.1 – 10.6] GHz unlicensed band for UWB
applications, many wideband antennas have been proposed
[1], [2], [3] and [4]. This technology has become very
popular in recent years and attracted more attention due to its
advantages such as low consumption, high data rate
transmission, immunity to multipath propagation and high
degree of reliability, etc. The UWB has found widespread
applications in communication systems [1], landmine
detection [2], radar systems [3], and biomedical applications
such as breast cancer detection [4], [5].
In the United States (US), the operating bandwidths for
communications released by FCC reach up to 7 GHz but the
FCC has limited the emission levels of UWB signals lower
than -41.3dB within the bandwidth as shown in Fig. 1 [6].
In general, the antennas for UWB systems should have
sufficiently broad operating bandwidth for impedance
matching and high gain radiation in desired directions. The
fractal antennas are preferred in UWB technology not only
because they are small and light weight or for easy
installation, but also because they have an extreme wideband
[7], [8], [9]. The Snowflake-Koch is a fractal shape which
was constructed by starting with an equilateral triangle. In the
first iteration, a triangle with side’s one-third unit long is
added in the center of each side of the original triangle (Fig.
2-a).
(a)
39 Hafid Tizyi et al.: Miniaturized Ultra Wideband Microstrip Antenna Based on a Modified Koch
Snowflake Geometry for Wireless Applications
(b)
Figure 1. The spectra released by FCC for commercial communications in
US: (a) for outdoor communication systems, (b) for Indoor communication
systems.
In the second iteration, a triangle with side’s one-ninth unit
long is added in the center of each side of the first iteration
(Fig. 2-b). Successive iterations continue this process
indefinitely.
Figure 2. The Koch Snowflake antenna: a) First iteration, b) Second
iteration.
In this paper, a high gain microstrip patch antenna based
on a modified Koch Snowflake geometry has been presented.
The antenna has been created by introducing techniques that
broadens the bandwidth. To increase the bandwidth of the
patch antenna, there are two methods.
The first one is coupling several resonances between them.
The equation (1) shows that when h increases, the bandwidth
also increases.
BW 3.77. . .
. (1)
The second method which is used in this paper is to reduce
the quality factor (Q) of a resonance (equation 2). To do so,
we can add an inductive (stubs), a capacitive element (slots)
or both of them. Also, by adding a lossy element or it can be
achieved by a progressive evolution of the impedance
between the feed-line and the radiating element.
(2)
With f res the resonant frequency
2. Antenna Design
The geometry of the Koch patch antenna is based on the
first iteration Koch Snowflake (Fig. 2-a). This antenna has
been designed using a 1.6mm thick FR4 substrate with a
relative dielectric = 4.4, which has a global dimensions of
3027 mm (W L). The dimensions of our proposed
antenna according to the Fig. 4 are shown in the table 1. W! and L! are the width and length of the feed-line. W! is
calculated using the equations (3), (4) [12], for , h =
1.6mm, and "# 50Ω.
(3)
"# '#()*+,,-./
0 1'.2321#.445 678/0 1'.999:
(4)
Table 1. Optimized antenna parameters.
Dimensions ;<=> ?<=> ?@ ;@ ?A
Value (mm) 30 27 11.6 3 2.7
Dimensions LB W L B W Value (mm) 11 1.2 1 18 3.59
Fig. 3 depicts the steps used to develop the antenna, by
introducing techniques that broadens the bandwidth
mentioned in the first section, namely:
1. Create a Fractal Koch Snowflake antenna (first iteration)
fed by a micro-strip line with a total ground plane (Ant. 0)
2. Add a rectangular element between fed-line and
radiation element (progressive evolution of the
impedance between the feed-line and the radiating
element) (Ant. 1).
3. Embed a slot element (Ant. 2).
4. Remove a top triangle of the fractal antenna (Ant. 3).
Ant. 0 Ant. 1
Ant. 2 Ant. 3
American Journal of Electromagnetics and Applications 2015; 3(6): 38-42 40
Figure 3. Steps required in the implementation of the proposed antenna.
Figure 4. Geometry and dimensions of the proposed antenna.
3. Results and Discussion
The antenna design simulation is done using the time
domain analysis tools from Computer Simulation Technology
(CST) Microwave Studio which provides wide range of time
domain signal that are used in UWB system. The numerical
analysis of the software tools are based on the Finite
Difference Time Domain (FDTD) [13]. For comparison
purpose, High Frequency Structural Simulator (HFSS) in
frequency domain since the numerical analysis is based on
the Finite Element Method (FEM) [14] is performed.
Fig. 5 illustrates the simulated results of the return loss for
the proposed antenna with the optimized parameters as listed
in table 1. We note that at 10dB, the antenna supports two
ultra widebands. In the first band, a good impedance
bandwidth of 6.55GHz is covered (3.4892 to 10.0392GHz),
while the second band covers 5.4976GHz (from 10.9013 to
16.3989 GHz).
Figure 5. Simulated reflexion coefficient for the proposed antenna.
Figure 6. Simulated reflexion coefficient for Ant. 0, Ant. 1, Ant. 2, and Ant. 3.
Parametric study of each element added to the original
antenna (Ant. 0) is presented in Fig. 6. As shown in this
figure, the addition of the rectangle element which allows an
adaptation of the impedance between radiation element and
feed-line, the partial ground plane and slots in rectangle
element allows increasing the bandwidth.
(a)
41 Hafid Tizyi et al.: Miniaturized Ultra Wideband Microstrip Antenna Based on a Modified Koch
Snowflake Geometry for Wireless Applications
(b)
Figure 7. Radiation patterns of the proposed UWB antenna (a): E-plane ,(b):
H-plane @ 3.6 GHz.
Antenna radiation pattern gives the radiation properties on
an antenna as a function of space coordinate. For linearly
polarized antenna, performance is often described in terms of
the E-plane (xy-plane) and H-plane (yz-plane) patterns [11].
Fig. 7 shows the two simulated dimensional E and H planes
at 3.6 GHz then Fig. 8 presents the E-plane and H-plane at
12.2 GHz.
(a)
(b)
Figure 8. Radiation patterns of the proposed UWB antenna (a): E-plane ,(b):
H-plane @ 12.2 GHz.
We can see that the antenna has nearly good
omnidirectional radiation patterns at all frequencies in the E
and H-planes. This pattern is suitable for applications in most
wireless communication equipment. Excepted, the antenna
exhibits directional orientation in H-plane at 12.2GHz.
The simulation group delay and Gain of the proposed
antenna is shown in Fig. 9. Group delay is an important
parameter in the design of the UWB antenna since it gives
the distortion of the transmitted pulses in the UWB
communications. For good pulse transmission, the group
delay should be almost constant in the UWB [10].
Figure 9. Group delay and Gain for the proposed antenna.
As it can be seen, the variation of the group delay for the
proposed antenna is almost constant for the entire UWB,
except for a sharp change in the first band at 4.3GHz. This
confirms that the proposed UWB antenna is suitable for
UWB communications.
Gain of over 2dBi over the whole frequency band has been
obtained. The value of gain is greater than 5dBi in the
frequency range of 3GHz- 7GHz and 12.4Ghz-16GHz which
is sufficient for use in most UWB applications such as in
American Journal of Electromagnetics and Applications 2015; 3(6): 38-42 42
Ground Penetrating Radars (GPR) and in Breast Cancer
detection [3], [5].
4. Conclusion & Future Work
In this paper, a simple and compact UWB antenna, based on
the Koch Snowflake geometry is proposed. The antenna
supports two ultra widebands, the first band (3GHz -9.43GHz)
a good impedance bandwidth of 6.43GHz has been achieved.
While the second band covers 5GHz from 10.9GHz to 16GHz.
The simulated results of the proposed antenna, using the CST
Microwave Studio and HFSS tools, present a constant group
delay and an omnidirectional radiation patterns. These results
make this antenna a good candidate for UWB applications and
systems such as WiMAX II [3.4-3.6] GHz, IEEE 802.11y
[3.65-3.7] GHz and WLAN [5.15-5.35] GHz.
To complete this work, the realization of the proposed antenna
should be done to compare the measured and simulated results.
This work will be also completed by associating the proposed
antenna in an antenna array to improve the gain.
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